The present invention pertains to a fastening system for fixing a motor vehicle steering column assembly unit.
Such fastening systems are used, e.g., to fix preassembled steering column assembly units on the body of a motor vehicle within the framework of the final assembly. At the time of the preassembly of a steering column assembly unit, one or more fastening screws are screwed into a preassembly thread each, which is preferably formed in the housing of the steering column assembly unit. This offers the advantage that no individual fastening elements have to be kept ready at the body during the final assembly of the steering column assembly unit. Once the steering column assembly unit has been brought into its final position in the course of the final assembly on the body, the fastening screws are screwed into a second fastening thread. This fastening thread may be located either directly on the body structure of a motor vehicle or also in an extension of the preassembly thread on the steering column housing. The steering column assembly unit is clamped in the second case by a body-side bracket arranged between the preassembly thread and the fastening thread. Both designs of fastening make it necessary for the fastening screw to have its thread leave the preassembly thread before the screw enters the fastening thread with its first turns or the preassembly thread will be broken, i.e., destroyed during the entry of the fastening screw into the fastening thread.
Both assembly variants described have one major drawback with respect to a possible removal of the steering column assembly unit.
In the first variant, in which the fastening screw has exited completely from the preassembly thread, the difficulty arises that loosening of the fastening screw inherently means returning of the screw into the first preassembly thread. This return is very difficult because the pressing force can usually be introduced only axially in the longitudinal direction of the screw and is ruled out nearly completely under the normal conditions of disassembly. As a result, removal of the steering column is difficult.
In the second of the above-described variants, the preassembly thread is often already destroyed completely after the first installation of the steering column. This means that this thread has to be recut after the removal of the steering column, because it can no longer be used and the ability of the steering column to be mounted is consequently limited.
German publications DE 38 25 177 A1 and DD 145 811 each describe a fastening system. Both fastening systems are for fixing a first assembly unit to a second component, which has a fastening screw. A corresponding first preassembly thread is provided on the first assembly unit, in which the fastening screw is fixed after the preassembly. A fastening thread is provided on the second component for fixing the first assembly unit to the second component by means of the fastening screw, wherein the fastening screw has two threaded areas for preassembly and for fastening. The second threaded area, which is used for fastening and is facing away from the screw head, has a smaller diameter than the first threaded area, which is used for the preassembly and is adjacent to the screw head.
Furthermore, U.S. Pat. No. 3,478,639 shows a fastening screw in which the preassembly thread and the fastening thread have different pitches.
The primary object of the present invention is therefore to eliminate the above-described drawbacks of the state of the art and to provide a fastening system that guarantees the problem-free assembly and removal of a steering column assembly unit and can be handled without problems and can be manufactured at low cost.
According to the invention, a fastening system for fixing a motor vehicle steering column assembly unit includes a fastening screw with a first threaded area and with a second threaded area. A steering column assembly unit with a steering column housing is provided, in which housing a preassembly thread corresponding to the threaded area is provided. A fastening thread is formed, which is axially aligned with the preassembly thread and is separated from same in the preassembled state by a gap. A U-shaped clamp is provided, which is fixed on the steering column housing. A bracket of the motor vehicle body is disposed at the gap, after the final assembly. This is for connecting the steering column housing with the motor vehicle body. The fastening screw passes through an opening in the bracket in the form of a slot or a hole. On the side of the bracket facing away from the preassembly thread, it engages the fastening thread with its second threaded area. With this the clamp is deformed by the movement of the screw. The clamp is then in contact with the lateral surfaces of the bracket of the motor vehicle body with its two legs and thus clamps the bracket.
According to an advantageous variant, the fastening thread may be introduced into a weld nut welded on the clamp.
According to one embodiment of the present invention, it is suggested that the fastening screw with at least two threaded areas for preassembly and for fastening be made with different thread pitches. The preassembly and fastening threads on the first assembly unit (and, depending on the design, on the second component) as well as the threaded areas of the fastening screw are provided with corresponding, different pitches. The second threaded area, which is used for fastening and is facing away from the screw head of the fastening screw, has a smaller diameter than the first threaded area of the fastening screw. The first threaded area is used for the preassembly and is adjacent to the screw head.
This special design causes the preassembly thread and the fastening thread to perform a relative movement in relation to one another in the case of the simultaneous arrangement of the screw in both threads and a corresponding screw-in movement and thus they can ultimately bring about clamping forces that permit the fixation of the steering column assembly unit on an intermediate plate fixed on the body. Both the turns of the fastening thread and of the preassembly thread remain completely intact during the fastening operation, so that a problem free removal of the assembled components is possible at any time in a simple manner and at a low cost.
Depending on the application and the space conditions of the construction to be used, the fastening system may be designed such that the thread pitch of the first threaded area is greater or smaller than the thread pitch oft second threaded area of the fastening screw. This freedom, as to modifying the design, expands the possible applications of the fastening system to other technical areas. The present invention is not limited to the above-described special field of application of a steering column fastening.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.